How can I simplify this Taylor expansion?

[ninevolt]

I want to show this taylor expansion:

$$\frac{1}{\sqrt{1+{x}^{2}}} \rightarrow x^2$$


what I keep getting is something to the x^3 could some one please help me with this simple expansion?

 

[elabed haidar]

(1+x^2)^-0.5
= 1-0.25(X^2) there is no x^3 okay